A method for recovering metals from a spent dispersed catalyst originating
from a Group VIB metal sulfide catalyst containing at least a Group VB
and Group VIII metal for hydrocarbon oil hydroprocessing is disclosed. In
one embodiment, the method comprises the steps of: contacting the spent
dispersed catalyst with a leaching solution containing ammonia and air to
dissolve the group VIB metal and the Group VIII metal into the leaching
solution at sufficient temperature and pressure; forming a slurry
containing at least a group VIB metal complex and at least a group VIII
metal complex, ammonium sulfate and solid residue containing at least a
Group VB metal complex and coke; separating and removing the solid
residue containing ammonium metavanadate and coke from the pressure leach
solution (PLS); precipitating from the PLS at least a portion of the
Group VIB metal and at least a portion of the Group VIII metal by
controlling the pH at a pre-selected pH to selectively precipitate as
metal complexes the Group VIB and Group VIII metals.